The present invention relates to a method for reducing NOx of externally ignited, explosion-type internal combustion engines in which the externally ignited, explosion-type internal combustion engine is operated at an air ratio of λ>1 in a lean mode and the λ value of the fuel/air mixture is controlled by an engine control device.
For the purpose of reducing the NOx values in the exhaust gas of externally ignited, explosion-type internal combustion engines it is known to operate them with a lean mixture at λ>1. Because of the high average mass temperature in the combustion chamber during stationary operation, high λ values must be selected in order to achieve low NOx emission.
Difficulties arise during non-stationary operation, for example, during acceleration from low engine rpm (revolutions per minute), when the average mass temperature in the combustion chamber is lower than during stationary operation and the misfire limit moves toward lower λ values.
It is therefore an object of the present invention to control the λ value of an externally ignited, explosion-type, or gas, internal combustion engine that is always operated at a lean fuel/air ratio of λ>1, where λ is controlled by an engine control device of the internal combustion engine, such that, for the purpose of NOx reduction, the engine is operated close to the misfire limit.